1. Field of the Invention
The invention relates to polymethacrylates which are transesterified with polyetherdiols or amidated with polyetherdiamines and are subsequently functionalized at the ends, and to their use as dispersants for preparing aqueous pigment preparations.
2. Background of the Invention
In order to facilitate and to improve the dispersion of solids in liquid media it is common to employ dispersants, which at the same time are also intended to have a stabilizing effect on the resultant dispersions and to prevent reagglomeration or flocculation of the particulate solids. As surfactants, the dispersants promote wetting of the particulate solids to be dispersed, and aid in the disruption of agglomerates.
They are particularly important, for example, for the dispersion of pigments in the preparation of printing inks, paints and other coated materials and in the pigmentation of polymer compounds.
In addition, specific dispersants may act as compatibilizers to increase the compatibility between chemically different polymer types. This is of particular importance, for example, for the preparation of sheet molding compounds (SMC) and bulk molding compounds (BMC).
In the production of paints and other coating materials, wetting agents and dispersants facilitate the incorporation of pigments and fillers, which are important formulation constituents that significantly determine the visual appearance and the physicochemical properties of coatings. Optimum use requires firstly that these solids are distributed uniformly in paints and inks and secondly that the state of distribution, once attained, is stabilized. However, numerous problems may occur during the preparation and processing of aqueous pigment pastes:
difficulties in incorporating the pigments, poor wetting PA1 high viscosities of color pastes, paints and other coating materials PA1 sedimentation PA1 vertical separation of pigments (flooding) PA1 horizontal separation of pigments (floating) PA1 low degree of gloss PA1 low hiding power PA1 inadequate color strength PA1 poor shade reproducibility, shade shift PA1 excessive tendency of coating materials to run PA1 R.sup.1 is the radical of a conventional chain regulator or initiator which is free from active hydrogen atoms, PA1 R.sup.2 are identical or different alkyl radicals or alternatively, optionally, are substituted aryl radicals, perfluoroalkyl radicals or dialkylamino radicals, PA1 R.sup.3 are identical or different alkyl radicals or azyl radicals, PA1 R.sup.4 is an organic radical having at least one carboxylic acid or carboxylate function, PA1 X is oxygen or NH, PA1 a is from 4 to 20, PA1 b is from 20 to 100, and PA1 c is from 0 to 20, the ratio b/c being .gtoreq. about 4.
There has therefore been no lack of attempts to provide effective dispersing additives for solids, especially pigments. For example, water-soluble polyisocyanate adducts containing hydrophilic polyether chains (EP-A-0 731 148), acidic poly(meth)acrylates (U.S. Pat. No. 3,980,602, WO-A-94/21701), phosphate esters of polyalkylene oxide block polyesters (WO-A-97/19948) or alternating copolymers of vinyl monomers and dicarboxylic diesters (WO-A-96/14347, EP-A-0 791 024), especially copolymers based on maleic acid derivatives and vinyl monomers, are described for this purpose.
However, the use of such products is also associated with a multiplicity of disadvantages. Frequently, for instance, high levels of dispersing additives are required, the levels of paste pigmentation that can be achieved are unsatisfactorily low, the stability of the pastes and thus of their viscosity is inadequate, and flocculation and aggregation cannot always be avoided; in many cases, there is also a lack of consistency of shade following storage of the pastes and a lack of compatibility with various binders. In many cases the use of known dispersing additives also has an adverse effect on the water resistance or light stability of coatings and, moreover, provides additional stabilization of the unwanted foam which is formed in the course of the preparation in processing. Furthermore, owing to deficiencies in the compatibility of the dispersing resins in numerous vehicles, there is often an undesirable impairment of the gloss.
The phosphoric esters of amphiphilic block copolymers, in particular, are characterized by poor stability of the phosphoric ester group to hydrolysis. The water resistance of coatings prepared with these esters is also adversely affected. Furthermore, these acidic phosphoric esters generally require an addition of amine base--undesirable in the amount required--in order, for example, to establish the optimized pH of a coating system.